Adding checkstyle & code coverage verification

[snigdhasjg]

Description

1. As development goes, uniform coding style plays big role in maintenance.
2. Automated checks on code coverage

Steps to reproduce

Expected Behavior

1. Having a checkstyle in place so its easy to contribute, local IDE setup doesn't hamper.
2. Having a .editorconfig in place so IDE automatically formats according to coding style
3. Tests need to be verified and coverage published (could be as a badge, thinking out loud)
   Note: Initially we can't fail build if coverage goes beyond X%. Once tests are fixed, will have the check in pipeline

Actual Behavior

1. Many unoptimized imports
2. Unit tests doing nothing other than printing

Metadata

NA

Typesense Version: NA

OS: NA

[R-Sandor]

Have you guys considered something like https://github.com/diffplug/spotless?

Checkstyle is still very good though.